The lawmakers, including Sens. Ted Cruz, R-Texas, and John McCain, R-Ariz., on Monday filed an amicus brief in Wisconsin federal court, supporting Johnson’s challenge to the Office of Personnel Management rule on the issue. In response to a March 17 Justice Department request to dismiss the lawsuit, the GOP members argue that Johnson's case deserves to be heard.

“The unlawful executive action at issue in this case is not an isolated incident,” the 35-page brief states. “Rather, it is part of an ongoing campaign by the Executive Branch to rewrite the Affordable Care Act ('ACA') on a wholesale basis.” OPM regulations cause personal harm, the lawmakers contend, by conferring “special privileges” in the form of health insurance subsidies. Elected officials who “value their political credibility and their public reputations far more highly than any form of monetary compensation” have a “concrete professional and personal interest” in avoiding such entitlements, the brief states. They also claim OPM stretched the definition of "small employer" by designating congressional employees to enroll in the District of Columbia's Small Business Health Options Program (SHOP) plan.

Twelve senators and 26 members of the House signed on to the amicus brief, posted online here .

Johnson also filed his own 30-page answer to Obama's attorneys on Monday. His 30-page standing response is also posted online .

“Congress was clear: The misnamed Affordable Care Act required Congress and its staff to get its health coverage through the exchanges and to do it without a tax-preferred employer subsidy, like anyone else who will lose employer-sponsored coverage," Johnson said in a statement. "The administration’s rule violates this law. It is unfair to the American people and it is an offense against the rule of law.”